1. Field of the Invention
The present invention relates to a lock which is operated by a magnetic key and to a key for operating such a lock. One such lock is described in EP0024242.
2. Description of the Related Art
Briefly, in such locks a slide member carries a plurality of tumblers in the form of small cylindrical magnets (magnet pins) which are slidably received in bores in the slide member so as to slide transversely of the direction of movement of the member. In the locked position, the pins are attracted towards a magnetic plate so that they extend part way out of the bores and through apertures in a non-magnetic lock plate which is fixed in position and located between the slide member and magnetic plate. Hence the pins lock the slide member in position relative to the non-magnetic lock plate. To unlock the lock, a magnetic key is slid between the magnetic plate and slide member, and repels the pins so that they are pushed out of the apertures in the lock plate. The slide member is then free to slide relative to the lock plate. The key engages a flange on the slide member so that further movement of the key moves the slide to allow operation of the lock.
The code of the lock is governed by the number, position and polarity of the magnet pins relative to the lock plate. EP0024242 describes a system in which the code of the lock can be changed without dismantling the lock. A rotatable wheel mounted in the slide member carries a magnet pin allowing the pin to be moved between four positions which correspond to four respective apertures in the lock plate. To move the pin, a code changing key is inserted to repel the pins from the lock plate and then move the slide member to a position where the wheel can be rotated by a tool inserted through the outside housing of the lock.
It has been found that if the pin is not moved precisely into one of its four positions it may, when an attempt is made subsequently to operate the lock, be caught in another aperture provided in the lock plate as the slide moves relative to the plate. This can cause further rotation of the wheel but generally results in a spurious code for the lock and a special procedure is sometimes required to repel the pin from the aperture in the lock plate so that the proper code can be set. The system of EP0024242 works well in practice but is time consuming as it requires a special manual operation to change the lock code.
Many hotels now have lock systems in which the lock code is changed automatically for each guest. This is presently done only with electronic locks: by recoding them directly from a central computer at the hotel desk; or by giving the hotel guest a key which carries a different code to that used by the previous guest. In the latter system, the lock runs independently of the central computer and contains a battery powered microprocessor which is programmed to detect the key code. If the code falls in the appropriate position in a list of codes carried in the lock memory the lock will be operated by the key. This system minimises difficulties caused by power failures but requires that a computer at the hotel desk be kept in synchronism with the code changes of all the independent locks at all times so that the hotel management knows which key to issue to a subsequent guest. Errors occur frequently in this system particularly due to electronic malfunctions, which requires resetting of locks that get out of sequence.